DRAINAGE OF IRRIGATED SHALE LAND. 
For the first year the discharge 
from this drainage system averaged 
43 gallons per minute, or about 
0.095 of a cubic foot per second, 
practically the entire quantity of 
which was collected by the 35 relef 
wells in about 1,000 feet of tile. 
The hydrograph shown in figure 11 
was plotted from measurements at 
the outlet of the system made at 
irregular intervals during the first 
14 months after the drains were in- 
stalled. It indicates the discharge 
in gallons per minute and shows 
a marked seasonal fluctuation. As 
determined from this hydrograph, 
the flow from the relief wells has 
averaged 1.2 gallons per minute 
per well. The quality of the drain- 
age water is indicated by analyses 
F and G in Table I. 
Considering the size of the af- 
fected area, the quantity of water 
developed is unusually large for 
this type of land, and would indi- 
cate the source of supply to be 
either leakage from the canal one- 
half mile north or the seepage of 
water supplied on not less than 20 
or 30 acres of the higher-lying 
lands in the neighborhood. In 
either case, before reaching the 
drains the water must pass through 
shale for several hundred feet. 
While the upper 34 feet of soil on 
this tract has been dried out thor- 
oughly, the efficiency of the drain- 
age system would have been in- 
creased by installing the main 
drain up the backbone of the shale 
ridge 8 feet deep instead of 6 ; more- 
over, another lateral drain with 
relief wells is needed, beginning 
400 feet north of the outlet of the 
system, where the main tile line 
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